The present invention relates to a tracheal ventilating device, especially a tracheal tube or tracheal cannula which obturates the trachea as hermetically as possible for ventilating a patient, the device comprising a cuffed balloon which blocks the trachea below the glottis and through which a ventilating cannula is passed, the cuffed balloon when filled or inflated and freely unfolded without any limitation, being larger than when placed in the trachea in an inflated state, and being made from a soft flexible foil material.
In a tracheal tube of such a type as is known from DE 196 38 935, it is suggested that a foil-like, extremely expandable material should be used for the cuffed balloon, the material closely nestling on the trachea or the local structures of the subglottic larynx. To optimize the tamponade of the subglottic space, it is recommended that the cuffed balloon should be pre-formed in accordance with the morphology of the space to be filled. An undesired draped fold is thereby to be avoided. It is to be ensured that the foil closely rests on the trachea so that no secretion passes from the pharyngeal space into the lung, if possible. A microaspiration of secretion beyond the cuffed balloon is thereby reduced considerably.
Secretion which passes into the distal trachea-bronchial system is the reason for the development of most of the ventilation-associated pneumonias.
In the tracheal tube suggested in DE 196 38 935, the cuffed balloon is elastically expanded while being inflated, and closely nestles on the wall of the trachea without any draped fold. When the filling pressure of the cuffed balloon exceeds the blood flow pressure of the vascular bed supplying the film of the mucous membrane, serious structural lesions of the epithelium might ensue. Above all with patients intubated for a long period of time, the filling pressure prevailing in the cuffed balloon should be kept at a level which is as low as possible and does not impair mucosal perfusion. By contrast, if the filling pressure is chosen such that it is too low, this might lead to a leakage of bacterially contained pharyngeal secretion beyond the cuffed balloon, resulting in a contamination and infection of pulmonary tissue.
It has therefore been suggested for long-term intubation that use should be made of cuffed balloons which unfold at a moderate filling pressure in the trachea without the cuff coat itself having to be expanded. The diameter of the freely unfolded cuffed balloon is here greater than that of the trachea to be closed. The residual amount of the cuff coat is turned into folds during the tracheal blockage of the cuff. On the other hand, however, it has been found that such cuffs have a high permeability to pharyngeal secretion, which means an increased risk of pneunomia. The leakage of secretion of said cuffed balloons is in the range of milliliters per second, which even corresponds to a macroaspiration in quantitative terms.
Therefore, it must be assumed that conventional cuffed balloons cause most of the pneumonias frequently observed in patients who are ventilated for a long period of time (incidence: 10% to 80%, depending on the respective patient).
It is the object of the present invention to improve a tracheal tube of the above-mentioned type in such a manner that a patient can be intubated as gently as possible at low pressures over a long period of time and that the risk of infection is low.
According to the invention this object is achieved with a tracheal tube of the above-mentioned type which is characterized in that the draped fold of the cuffed balloon rests on the trachea and is designed in such a way that the loop formed at the dead end of a fold has a small diameter which inhibits the free flow of secretion through the loop of the fold.
The sealing capacity of the cuff can thus be improved considerably; the risk of ventilation-associated pneumonia is reduced accordingly.
Surprisingly enough, the flow of secretion can be influenced by a specific design of the cuff folding in the area of the loop of the fold, i.e. at the base of the fold. While in the prior art it has so far been assumed that cuffed balloons with a draped fold cannot rest on the trachea in a sufficiently tight manner because of the low filling pressure, the invention shows a method of inhibiting the flow of secretion, the method being employed in the area of the loop of the fold. When the diameter of the loop is sufficiently small at the base of the fold, the free flow of secretion through the loop is inhibited. When the cuff is blocked, the resultant loops at the deep end of the fold can be reduced with respect to their diameter, for instance by selecting the material or the foil thickness, in such a manner that the flow of secretion is decelerated or, ideally, stopped altogether.
This is surprising because leakage has always been regarded as a problem of pressure. A constructional change in the draped fold has so far not been considered yet.
Preferably, the loop is given a capillary size. This will then result in adequate adhesion forces of the secretion on the loop and in a sufficient viscosity-dependent resistance of the secretion to reduce the flow of secretion. The flow rate in the capilary-sized loop is then smaller than the theoretically possible rate without adhesion or viscosity forces, so that a smaller amount of secretion will flow therethrough in the course of time. In an optimum case the diameter of the loop is made so small that the flow of secretion is stopped altogether.
The diameter of the loop may be less than 0.1 or 0.05 mm in an especially advantageous development. At a value below 0.1 mm a certain inhibition of the flow rate of the secretion through the loop can already be observed. At a loop diameter of less than 0.05 mm, the flow of secretion is further decelerated and almost stopped.
Advantageously, the wall thickness of the foil material can be chosen to be so small that the inner radius of the developing loops is reduced at physiologically tolerated filling pressures to such an extent that the free flow of secretion is prevented. The more flexible and thinner the material is, the smaller is the diameter of the loop.
The wall thicknesses of conventional cuffed balloons predominantly range from 0.06 to 0.1 mm.
It is suggested that the wall thickness of the foil should be slightly smaller than or equal to 0.02 mm. When the cuffed balloon is made from such a foil, the flow of secretion through the loop will already be inhibited at a standard filling pressure.
In a variant of the invention, the wall thickness of the foil is approximately 0.01 to 0.005 mm. In the case of a wall thickness ranging from 0.01 to 0.005 mm, a soft flexible foil will already inhibit the flow of secretion in a satisfactory manner and the stasis thereof will be achieved in the area of the base of the fold, respectively.
Foils of presently available materials having wall thicknesses of less than 0.005 mm are not sufficiently tear-resistant for the cuffed balloon which is designed according to the invention. If suitable and sufficiently resistant materials are available, foil thicknesses below 0.005 mm should be aimed at for achieving optimum sealing characteristics.
According to a preferred embodiment the foil material of the cuffed balloon may e.g. consist of polyethylene teraphthalate (PETP), low-density polyethylene (LDPE), polyvinyl chloride (PVC) or polyurethane (PU). These materials are body-tolerated and, when being processed into correspondingly thin walls, are especially suited for forming a hermetically obturating draped fold. Copolymer admixtures for modifying the characteristics of the material are possible (e.g. LDPE-EVA).
The cuffed balloon possibly consists of a material which adheres to itself and the adhesion of which helps to reduce the clear diameter of a loop at the base of the fold.
In a variant of the invention, the wall thickness of the foil may be thinner in the area of the draped fold than in the fold-free area directly adjacent to the tracheal mucous membrane. Folds are preferably formed in the thin-walled cuff region because the foil can more easily be deformed in said area. The foil base can form loops of a smaller diameter because of the smaller wall thickness. In the more thick-walled cuff region between the folds the cuff coat has characteristics that are slightly more rigid so that it only rests in a rounded form on the wall of the trachea.
In a particular manner the fold walls which are opposite to each other in a fold are interconnected in the area near the base of the fold. The point of connection may be provided directly next to the forming loop so that the size of the loop is set by said point of connection to a desired diameter.
Preferably, the opposite fold walls can be interconnected at the dead end of the fold to fill the loop, whereby the flow of secretion is reliably prevented. It is also possible to weld or glue the opposite fold walls of a fold to each other.
Particularly, a fold section having a variable cross-section in the depth of the fold, in which the opposite fold walls are not materially interconnected, may be adjacent in the fold to the connection portion of the opposite fold walls. The cuffed balloon can adjust itself to the trachea in size and shape via such a pre-formed draped fold having a variable fold depth, i.e. in accordance with the concept regarding the residual cuff coat.
In a tracheal tube of said type, which is known from DE 196 38 935, it is suggested that the conventional cuff of the tracheal tube should be supplemented by a second tampon balloon which directly follows the cuff to the oral side and completely fills the so-called subglottic space (space between the upper edge of the cuff and the vocal cords). The tampon balloon consists of a foil-like, extremely expandable material which closely nestles on the local structures of the subglottic space under expansion. To optimize the tamponade of the subglottic space, it is recommended that the balloon should be pre-formed in accordance with the morphology of the space to be filled. A fold-free surface of the tampon balloon which is as smooth as possible is to prevent any accumulation of secretion and the formation of a subglottic germ reservoir, respectively.
However, the expansion of such a displacement body is accompanied, above all in the region of the morphologically complicated inner larynx, with the formation of pressure peaks in the area of prominent structures that extend into the local space. When the filling pressure of the tampon balloon exceeds the perfusion pressure of the vascular bed supplying the film of the mucous membrane, serious lesions of the wall structures may ensue, above all in the region of the dorsolateral subglottic larynx.
To prevent the larynx from being damaged by pressure, it is recommended that the tampon balloon should also be provided with a residual volume, i.e., its volume in the freely unfolded state should exceed the volume of the inner larynx to be filled. The tampon balloon complies with the inventive principles governing the design of a sealing and gentle cuffed balloon. The formation of the above-described capillary-like structure is thereby prevented.
Since a lot of applications require a reliable and mechanically loadable anchorage of the tracheal tube within the windpipe, a certain minimum wall thickness of the fixing cuff must not be exceeded, depending on the respective quality of the material. Despite a substantial reduction of the wall thickness, the formation of fluid-draining loops cannot adequately be prevented in all cases.
Nevertheless, in order to ensure optimum sealing characteristics, the present invention suggests that the mechanically fixing cuff should be supplemented by an additional sealing tampon balloon complying with the above-described principles of design that govern sealing aspects and tissue compatibility. The tampon balloon can be subjected to a minimum filling pressure of preferably 10 to 15 mbar which has only the function to unfold the thin, sealing balloon wall.
As for its arrangement and relation with respect to the tube shaft or the fixing cuff, the tampon balloon may correspond to the embodiments described in DE 196 38 935.
It is suggested that the fixing cuff should be mounted at the caudal side of the device, and the tampon balloon relative thereto at the cranial side. During intubation the fixing cuff is pushed forwards beyond the cricoid cartilage of the larynx, preferably into the region of the middle tracheal third where it is anchored in a reliable and tracheally compatible manner. The tampon balloon which is arranged at the cranial side relative thereto can expand in the direction of the subglottic space where, being arranged upstream of the fixing cuff, it obturates secretion seeping from the pharynx.
The fixing cuff and the tampon balloon may also be positioned in sequential order on the ventilating cannula. The tampon balloon while expanding to the cranial side can partly cover the so-called subglottic space up to the glottic plane or slightly beyond said plane. Since both balloons are filled separately via corresponding supply lumina mounted inside the tube shaft, the functions of fixing cuff and tampon balloon in the case of a serial arrangement can largely be controlled independently of each other.
Preferably, the point of connection between the two serially arranged balloons is configured such that no secretion can accumulate in the area thereof in the filled and tracheally unfolded state.
Advantageously, the fixing cuff can be enclosed by the tampon balloon at least in portions, preferably completely. The outer tampon balloon can thus expand to the caudal side up into a variable area of the fixing cuff. The formation of a germ reservoir between the balloons is thereby prevented.
In a preferred variant, the cuff which tracheally fixes the tube is entirely surrounded by the tampon balloon. The tampon balloon extends from the caudal end via the cranial end of the cuff into the so-called subglottic space and into the area of the vocal cord plane or slightly beyond said plane. In this interposed embodiment regarding the combination of a fixing cuff with a tampon balloon, the invention suggests a particular mode of handling.
After conventional intubation the outer liquid-obturating tampon balloon is initially to be filled and is to nestle on the wall of the local space to be filled at a minimum pressure. Subsequently, the fixing cuff arranged in the interior is then unfolded in the customary manner and at the standard filling pressures for stabilizing the tube in the trachea. Hence, the fixing cuff has no fluid contact, i.e., the possible formation of loops in the coat of the inner cuff has no fluid-draining effect.
To prevent the two balloons from adhering to each other while unfolding, and to ensure their independent mechanical characteristics during ventilation, it is suggested that a small amount of a separating medium, such as oil or talcum, should be introduced into the space between the balloons.
When the tampon balloon which is subjected to a minimum pressure that is gentle on the tissue is expanded into the region of the glottis or slightly beyond said region, the potential path of entry for germ-containing secretion is extended to a maximum. The volume of secretion is reduced by the displacing tampon balloon to a small film exposed to the epithelium-inherent defense factors and is thus reduced with respect to its flow rate to a maximum degree. On the whole, the efficiency of the local defense mechanism is thereby optimized considerably.
Since the stasis of germ-containing material above the tracheally fixing cuff is suppressed virtually completely, changes in the mucous membrane due to chronic inflammation can additionally be prevented.
When the tampoon balloon extends beyond the vocal cords into the supraglottic region, the permanently traumatized contact of the tube shaft with the vocal cords can be reduced by the tension-free lining of the vocal cords with the coat of the tampon balloon.
Every conventional tube (high-volume/low-pressure, high-pressurellow-volume cuff or intermediarily designed cuff) that does not, as preferred above, eliminate the subglottic germ reservoir can be optimized with respect to tightness and tissue compatibility by the interposed arrangement of the fixed cuff and by a tampon balloon having a wall thickness of only a few micrometers. The outer tampon balloon should only slightly exceed the fixing cuff as to its cranial and caudal extension or should dimensionally correspond to the fixing cuff. The two balloons can be filled separately. In this case, too, the outer, hermetically obturating cover which has a thickness of only a few micrometers is to prevent by way of its initial unfolding that the formation of fluid-conducting tubuli of the inner cuff with the greater wall thickness causes a leakage of secretions.
Such an arrangement of a sealing and stabilizing coat or envelope makes the invention applicable not only to tracheal tubes, but also in particular to tracheal cannulas. Tracheal cannulas are inserted not via the larynx, but via a surgically laid opening (stoma) in the windpipe.
The maintenance of the filling pressure in all of the above-described cuff and tampon balloons is ensured by an extracorporeally mounted reservoir. In accordance with the Lanz principle, such reservoirs may be equipped with a self-regulating valve mechanism, or may be designed in the manner of simple valve-carrying reservoir balloons.
To be able to estimate the desired filling pressure, an imprinted figure or a specific form of the reservoir balloon may be chosen which specifically varies in a corresponding filling state.
To prevent pressure variations inside the trachea or the larynx from effecting an expansion of the wall structures, the material compliance of the reservoir balloon should not exceed that of the cuff or tampon balloon.
The supply legs leading to the tampon balloon should be chosen such that they have a sufficiently large lumen so as to effect a rapid pressure compensation.
Any suitable fluid may be used for filling the sealing or fixing cuffed balloons.
Moreover, when liquids are used, a valve mechanism can be dispensed with and the filling operation can solely be controlled via an open liquid column.
The inventive seal of the tracheal or laryngeal remaining lumen (which is created during intubation) by way of a reduction of the wall thickness of the cuff coat to the range of a few micrometers also permits the liquid-tight tamponade of the intubated trachea of neonates, babies or infants.
On account of the high tissue vulnerability with respect to conventionally cuffed balloons, all kinds of sealing devices have so far been dispensed with during intubation. A tissue-compatible, liquid- or gas-tight sealing of the extremely sensitive upper airways would be possible by way of an elongated tampon balloon which fills the trachea and the larynx and is subjected to minimum pressures (preferably of 5 mbar).